A demand for low dielectric properties (low specific dielectric constant, low dielectric dissipation factor) in a high frequency region has recently increased for a flexible printed circuit board material in association with an increase in a speed and an increase in a frequency of a transmission signal in a flexible printed circuit board. Conventionally, a polyimide film and a polyethylene terephthalate film and the like are used as a substrate film in the flexible printed circuit board. For example, substrate films having low dielectric properties such as a Teflon (registered trademark)-based material (see Patent Literature 1), a liquid crystal polymer-based material (see Patent Literature 2), and a cycloolefin-based material (see Patent Literature 3) have been proposed.